1. Field of the Invention
The invention relates to a rivet for connecting workpieces, in particular a blind rivet, having a sleeve with a shank and a widened preformed head and optionally a rivet mandrel with a head. An end of the shank lying opposite the preformed head can be deformed to form a driven head by drawing the rivet mandrel into the sleeve.
2. Discussion of Background Information
When it is a matter of connecting metal sheets or plates to one another, rivets often represent the connecting elements of choice. This applies in particular when parts made of different materials are to be connected to one another and a welding, soldering or adhering is not possible or leads only to unsatisfactory results. As a result, rivets with which heavily loadable, durable connections can be achieved are primarily in demand.
In a very simple and customary form, rivets are embodied in one part as sleeve-shaped hollow rivets with a hollow shank and a widened preformed head connecting thereto. To embody a placed rivet, it is then necessary only to deform the end of the shank lying opposite the preformed head through the application of force to form a driven head. Rivets of this type are also used in particular for connecting non-metallic materials. However, this is possible only when the workpieces are accessible from both sides. Otherwise, one must rely on blind rivets.
Blind rivets are constructed in a multiple-part manner. On the one hand, a blind rivet similar to a pop rivet comprises a sleeve with a hollow shank, which at one end has a widened preformed head. On the other hand, a blind rivet in addition requires a rivet mandrel, so that a driven head can be formed despite restricted accessibility to the workpieces on one side. The rivet mandrel is shaped cylindrically, for example, and has a widened head, the outer diameter of which corresponds at most to an outer diameter of the shank. The rivet mandrel is thereby dimensioned such that it can be inserted into the hollow shank of the sleeve and drawn in through it. The rivet can then be inserted and placed from one side. During placement, the widened head of the rivet mandrel comes to bear against the end of the sleeve lying opposite the preformed head and deforms this end to form a driven head due to the tensile force applied or a force acting on the shank.
A use of rivets of this type for producing connections between workpieces presupposes that corresponding bores for accommodating the rivets are inserted into the workpieces. These bores should be sized such that after placement a shank of the sleeve bears against the bore walls over the whole surface as far as possible. Otherwise, if this is not the case, the workpieces have a play towards the shank or the sleeve, which with higher thrust forces means that the rivet connection is loosened and ultimately fails prematurely, in particular with alternating loads.
However, problems arise with reference to this need for a production as exact as possible of bore diameters to accommodate a sleeve: one particular problem is that it is difficult to insert bores into various workpieces when the bore diameters are to differ only within a permissible tolerance of a few hundreds of a millimeter, in particular when they the workpieces comprise different materials. This problem becomes evident in particular when for individual constructions, for example, in aircraft construction, many thousands of rivets are to be placed and accordingly many bores are to be provided.
In the case of blind rivets, the above problem is even more severe. As mentioned, blind rivets are used when the workpieces to be connected are accessible from only one side. In order for it to be possible to insert rivets of this type into the bores before placement, an outer diameter of the head of a rivet mandrel may correspond at most to a maximum outer diameter of the shank of the sleeve. For this reason a diameter of the rivet mandrel head is limited, which can have an unfavorable effect on a non-positive closure between the workpieces (low surface pressure). With loads, a release of a connection is therefore more easily possible and an exact production of bore diameters is all the more important.
To solve the above problem it has already been suggested to ream out bores and thus to bring them to approximately the same diameter. Although this can be seen as a useful approach in order to achieve connections with higher loading capacity, it is a disadvantage that reaming operations require a high labor expenditure and in particular in customary fields of application for rivets, for example, in aircraft construction, therefore appear to be extremely impractical.